This article by Edmund Standing should be compulsory reading. Standing does a great job of exposing the totalising narrative of the far left, with its quasi-religious apocalypticism and its comprehensive prescriptions for human behaviour. Not all religious positions are dangerous to our liberties (the syncretic polytheism of the ancient Romans wasn't so bad, for example), and not all dangerous ideologies are religious in the sense of postulating supernatural entities. However, many current religious positions endanger our freedoms because they have strong totalitarian, dogmatic, apocalyptic tendencies, and they attempt to use the power of the state to suppress contrary views. These positions should be critiqued and resisted. The same applies to quasi-religions such as Marxism and Nazism.
In this case, we see hardline Marxists attempting to characterise any criticism of Islam, as a body of beliefs and sanctioned practices, as something akin to racism. It is nothing of the sort.
Hardline Marxists are not friends of liberal secularists. Marx did have some worthwhile sociological insights, but a dogmatic and comprehensive Marxist worldview shares all the worst characteristics of the monotheistic religions.